This invention relates to a process for the deposition of silicon, and more particularly to the efficient utilization of silicon bearing effluent in a step-wise silicon deposition process.
Large quantities of high purity silicon are provided for the semiconductor industry by the hydrogen reduction of a silicon-bearing reactant on a heated substrate. In the typical process, for example, trichlorosilane and hydrogen are reacted in a bell jar to deposit silicon on a heated rod such as a rod of pure silicon. The process is highly inefficient in the utilization of available silicon, with only about one-eighth of the available silicon actually depositing on the heated rod. The effluent from the reaction contains the remaining seven-eighths of the available silicon in the form of silicon tetrachloride, small quantities of dichlorosilane, and unreacted trichlorosilane. This silicon-bearing effluent is normally separated by fractional distillation; the silicon tetrachloride is discarded or used as a low value by-product, the dichlorosilane is used in other reactions such as epitaxial deposition, and the trichlorosilane is purified and reused for further silicon deposition. The separation process is costly, time-consuming, and fails to utilize a large fraction of the available silicon.
In view of shortcomings of the aforementioned conventional silicon deposition process it is an object of this invention to provide an improved silicon deposition process.
It is a further object of this invention to provide an improved process for the deposition of silicon which more fully utilizes the silicon available in the input reactants.
It is another object of this invention to provide an improved silicon deposition process having controlled growth parameters.
It is still another object of this invention to provide an improved silicon growth process in which equilibrium is achieved between reaction input and effluent.